Personal protective gear has come into use in many areas in order to protect the user from hazards. For example, members of firefighting crews and technical relief organizations are equipped with protective gear in order to be able to be deployed during their missions without hazards or with reduced hazard. Personal protective gear is also used in the area of workplace protection, for example, when handling chemicals. Further applications pertain, for example, to devices known as closed-circuit devices, in which the carbon dioxide expired by the user is removed from the breathing air.
Other fields of application of protective gear pertain to medical staff, which shall be protected from infectious diseases while in contact with patients.
The removal or abatement of gaseous harmful substances from gas flows is described, in general, as a mass transfer process and is of prominent significance especially in the area of personal respirators. In conjunction with breathing masks, escape hoods, closed-circuit or regeneration type respirators, filters and/or filter inserts protect the human user from vapors and gases that are hazardous to health.
The harmful substances are either retained in this case in corresponding absorbents or adsorbents or converted by chemical reactions into harmless substances.
One example of the chemical conversion of undesired or harmful substances into harmless substances is the processing of breathing gas in closed-circuit or regeneration type respirators by the use of so-called breathing lime, which binds the expired carbon dioxide.
Breathing lime is also used, besides in the said respirators, in the area of medicine in anesthesia apparatuses and respirators. Anesthesia apparatuses shall be mentioned, in particular, in this connection, in which the breathing air mixed with an inhalation anesthetic is inspired and then expired by the patient in a closed circuit, while the carbon dioxide present is bound or removed by the use of breathing lime.
Harmful expired CO2 is chemically bound on the absorbent in these applications, e.g., in a chemical reaction, as it appears clearly from the following reaction equations. Water as well as heat are generated as a result with a reaction enthalpy of ΔHR=−113 kJ/molCO2+H2O→H2CO3 H2CO3+2NaOH→Na2CO3=2H2ONa2CO3+Ca(OH)2→CaCO3+2NaOHCa(OH)2+CO2→CaCO3+H2O
One example for the retention of undesired or harmful substances by corresponding adsorbents is the use of activated carbon as a respirator filter material.
As is known in industry, activated carbon consists of carbon with a highly porous structure. The inner surface is said to be 300 to 2,000 m2 per g of carbon. The harmful gases become attached to the inner pores of the activated carbon, and the adsorption properties depend on the pore size distribution.
Absorbents and/or adsorbents for cleaning gases, which are used in the area of personal respirators, are produced in various granular forms. The granular material guarantees a sufficiently large reaction surface for the gas cleaning with at the same time a sufficiently low flow resistance of a filter cartridge filled with absorbent/adsorbent.
The formation of ducts within the granular material filling or at the edges towards the cartridge must be prevented from occurring by all means in the filled cartridges or filter cartridges when granular materials are used. Such ducts may very greatly reduce the performance of such a filter and thus potentially jeopardize the user.
The cause of such duct formation may be an unintended relative motion of the particles of the granular material among each other.
Another undesired effect of the relative motion is the abrasion of the absorbent/adsorbent, which occurs in the process. The abrasion dust must possibly be removed in a complicated manner after longer shipping before the use of the absorbent/adsorbent.
The user's health may possibly be jeopardized if larger quantities of dust enter the user's airways.
To fill the filter cartridges/absorber containers, the absorbent granular materials and/or adsorbent granular materials are filled typically through sieves, which affect the motion of the falling particles of granular material such that a maximum bulk density is obtained depending on the particle size. The inlet and outlet openings are then closed by relatively rigid sieves or sieve plates. The compression forces applied by the sieves on the granular material filling limit the relative motion of the particles of granular material.
A corresponding device is described in the document DE 39 17 096 C1. A container for a chlorate candle is shown in this document, which is filled with a granular chemical and has a bottom plate, which is pressed against the chemical by means of a spring.
However, the drawback of such a solution is that the compression forces cannot be applied uniformly to the filling and can be completely abolished by friction between the particles.
Another drawback is that the inlet and outlet are closed with sieves, which leads to an impairment of the flow through the absorber filling.
The packing density of the bulk material may be reduced by storage, which is often associated with a shrinkage of the particles, as well as by shipping.
Other solutions are based on filter bodies made of multilayer fabric and/or knitted fabrics, which is manufactured from fibrous material and/or wire or open-cell plastic foam or nonwoven. The particles of granular material are then bound in these filter bodies, for example, with adhesives or adhesive liquids.
European Patent EP 0 387 394 B1 describes a process for producing a filter body with the use of an adhesive liquid.
European Patent EP 0 339 487 A2 discloses an activated carbon layer for gas masks as an air-permeable flat object with a granular layer or a layer consisting of beads consisting of activated carbon, which are bound to the flat object with hot melt adhesive.
European Patent Application EP 0 294 707 discloses a breathing mask made of filtering material in the form of an open-cell foam material, which contains the adsorber particles.
Patent Application WO 98/17375 discloses an absorber/adsorber body, which consists of a wound, furrowed adsorber mat, in which flow ducts are formed by the furrowing.
One drawback of these solutions is, on the one hand, the reduced efficiency of such filter bodies as well as the increased flow resistance. Another drawback is the complicated manufacture of such solutions. The lateral sealing against the wall of a filter cartridge likewise requires increased effort. In case of the absorber roll, mechanical damage to the roll, which cannot be ruled out, may possibly lead to so-called bypass flows and undesired breakthroughs of harmful substances.